1. Field of the Invention
The present invention relates to rotary compressors and, more particularly, to a rotary compressor of the low operational noise type, having a bypass passage on the internal surface of its cylinder at a position around a fluid exhaust stroke initiating point to effectively reduce excessive pressure pulsation generated at the initial stage of an exhaust stroke, thus effectively reducing impact exciting force caused by the pressure pulsation within the compression chamber of the cylinder and effectively reducing pulsation noise having a wide frequency band.
2. Description of the Prior Art
As well known to those skilled in the art, compressors are machines used for compressing fluid, such as liquid or gas, to a desired pressure and have been preferably and widely used for a variety of applications. Such compressors are recognized as very important elements in a variety of refrigeration systems, such as air conditioners or refrigerators, since the compressors are used for compressing refrigerant of refrigeration cycles and determine the operational capacities and operational efficiencies of such refrigeration systems. Conventional compressors have been classified into two types: rotary compressors and scroll compressors. Of the two types, the scroll compressors are designed to compress refrigerant by a rotating action of a rotatable scroll, operated in conjunction with a drive unit, relative to a fixed scroll. On the other hand, the rotary compressors compress refrigerant by a roller, which is operated in conjunction with a drive unit and is eccentrically rotated within the bore of a cylinder.
FIGS. 1 and 2 show the construction of a conventional rotary compressor. As shown in the drawings, the conventional rotary compressor comprises a casing 10 provided with both a refrigerant inlet port 10a for introducing refrigerant into the casing 10 and a refrigerant outlet port 10b for discharging compressed refrigerant from the casing 10. A stator 11 is fixed within the casing 10, while a rotor 12 is positioned to be electromagnetically rotatable relative to the stator 11 when it is electrically activated. A rotating shaft 13 having an eccentric portion (13xe2x80x2) is integrated with the central axis of the rotor 12 and is rotatable along with the rotor 12. A roller 17 is fixed to the eccentric portion (13xe2x80x2) of the rotating shaft 13 and set within the bore 16a of a cylinder 16. The cylinder 16 has a suction port 21 and an exhaust port 22 and compresses working fluid, sucked into the bore 16a through the suction port 21, in accordance with an eccentric rotating action of the roller 17 within the bore 16a and discharges the compressed fluid from the bore 16a through the exhaust port 22.
A vane 18 is provided within the bore 16a of the cylinder 16 at a position around the exhaust port 22 and is normally biased by a spring 19 so as to elastically come into contact with the external surface of the roller 17. The above vane 18 partitions the chamber, formed between the cylinder 16 and the roller 17, into a variable suction chamber 16b and a variable compression chamber 16c. An exhaust control valve (not shown) is provided within the exhaust port 22 of the cylinder 16 and is used for controlling the port 22 so as to allow the port 22 to exhaust the compressed fluid from the cylinder 16 when the roller 17 completely rotates within the cylinder 16 at a predetermined angle. A main bearing 14 is installed at an upper position within the cylinder 16, while a sub-bearing 15 is installed at a lower position within the cylinder 16.
The above conventional rotary compressor is operated as follows: That is, when the compressor is electrically activated, the rotor 12 is electromagnetically rotated along with the rotating shaft 13 relative to the stator 11. Therefore, the roller 17 is eccentrically rotated within the cylinder bore 16a while coming into tangential contact with the internal surface of the cylinder 16. When the roller 17 is eccentrically rotated within the cylinder bore 16a, refrigerant is introduced into the bore 16a through the suction port 21. The refrigerant is thus gradually compressed as the compression chamber 16c, formed by the roller 17, the internal surface of the cylinder 16 and the vane 18, is gradually reduced in its volume due to the eccentric rotating action of the roller 17 within the cylinder bore 16a. When the pressure of the refrigerant reaches a predetermined reference level as it is compressed, the exhaust control valve is opened, thus allowing the compressed refrigerant to be exhausted from the cylinder 16 through the exhaust port 22. The exhausted compressed air is, thereafter, discharged from the compressor through the refrigerant outlet port 10b formed on the casing 10 of the compressor.
In the drawings, the reference numeral 20 denotes an accumulator.
FIG. 3 is a sectional view corresponding to FIG. 2, showing a resonator installed within the cylinder of the conventional rotary compressor. As shown in the drawing, a resonator 40, designed to reduce operational noise of a predetermined frequency band, is formed in the cylinder 16 to communicate with the exhaust port 22. Due to the resonator 40, the compressor reduces pulsation noise, caused by refrigerant gas within the cylinder 16 during a refrigerant compression stroke of the cylinder 16. The resonator 40 also prevents an undesirable quick discharging of the pressure pulsation from the cylinder 16 during a refrigerant exhaust stroke of the cylinder 16, thus reducing operational noise and vibration during the refrigerant exhaust stroke. The resonator 40 is determined in its resonating frequency band in accordance with both the shape of a resonating cavity determined by the acoustic resonance and the shape of a pressure leading passage.
Since both the shape of the resonating cavity and the shape of the pressure leading passage are fixed, the resonating frequency band of the resonator 40 for the cylinder 16 is fixed. However, since the compression chamber 16c is gradually reduced in its volume in a refrigerant compression stroke, the internal pressure of the compression chamber 16c continuously varies, with the pressure pulsation being exhausted from the cylinder 16 through the exhaust port 22. Therefore, the compressor inevitably generates operational noises having a variety of frequency bands, and so the resonator 40, having a fixed resonating frequency band, does not desirably reduce the pressure pulsation in the compressor.
In addition, lubrication oil may be undesirably introduced from the cylinder bore 16a into the resonating cavity of the resonator 40 at the initial stage of the operation of the compressor. In such a case, it is almost impossible to effectively remove the lubrication oil from the resonator 40 during the operation of the compressor since the pressure leading passage of the resonator 40 is positioned above the resonating cavity. The amount of lubrication oil, remaining in the resonating cavity, varies during the operation of the compressor, and changes the noise reduction characteristics of the resonator 40. Therefore, the resonator 40 does not maintain its designed noise reductirefrigeranton characteristics and fails to accomplish its desired noise reducing operational effect.
In addition, since the resonator 40 is formed on the middle portion of the exhaust line while communicating with the exhaust port 22, the quantity of refrigerant, which is undesirably remained in the compression chamber 16c at the final stage of a compressed refrigerant exhaust stroke and is free from exhausting compressed refrigerant from the cylinder 16, is undesirably increased. Therefore, the highly compressed refrigerant gas, remaining in the dead cavity, is undesirably fed back to the suction chamber 16b of the cylinder bore 16a after the exhaust stroke, thus causing a re-expansion of completely compressed refrigerant and deteriorating the compression efficiency of the compressor.
Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide a rotary compressor of the low operational noise type, which has a bypass passage on the internal surface of its cylinder at a position around a fluid exhaust stroke initiating point to effectively reduce excessive pressure pulsation generated at the initial stage of each exhaust stroke, thus effectively reducing impact exciting force caused by the pressure pulsation within the compression chamber of the cylinder and effectively reducing pulsation noise having a wide frequency band.
In order to accomplish the above object, the present invention provides a rotary compressor comprising a casing, a rotating shaft set within the casing, a roller eccentrically fixed to the rotating shaft and eccentrically, rotatably set within a cylinder so as to form a variable suction chamber and a variable compression chamber within the cylinder, further comprising a bypass passage formed on the internal surface of the cylinder at a position around the refrigerant exhaust stroke initiating point, thus allowing the compression and exhaust chambers to communicate with each other through the bypass passage at the initial stage of each exhaust stroke.